The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete...
Cement & Concrete Composites 23 (2001) 47±56 www.elsevier.com/locate/cemconcomp Resistance to biogenic sulphuric acid corrosion of polymer-modi®ed mortars A Beeldens a,*, J Monteny b, E Vincke c, N De Belie d, D Van Gemert a, L Taerwe b, W Verstraete c a Department of Civil Engineering, Catholic University Leuven, W de Croylaan 2, 3001 Leuven, Belgium Department of Civil Engineering, University of Gent, Technologiepark-Zwijnaarde 9, 9052 Gent, Belgium c Laboratory of Microbial Ecology and Technology, Univerisity of Gent, Coupure L 653, 9000 Gent, Belgium Laboratory for Agricultural Machinery and Processing, Department of Agro-engineering and -economics, Catholic University Leuven, Kard Mercierlaan 92, 3001 Heverlee, Belgium b d Received 22 December 1999; accepted July 2000 Abstract The use of polymer-modi®ed mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modi®cation Prior to the durability tests, experimental research is carried out to reveal the in¯uence of polymer modi®cation on the physical and mechanical properties of mortar and concrete The results of this research are presented in this paper Due to the interaction of the cement hydrates and the polymer particles or ®lm, an interpenetrating network originates in which the aggregates are embedded The density, porosity and location of the polymer ®lm depend on the type of polymer emulsion and on its minimum ®lm-forming temperature (MFT) If air entrainment is restricted, an increased ¯exural strength is measured Scanning electron microscope (SEM) analyses reveal the presence of polymer ®lm and cement hydrates in the mortar The polymer ®lm causes a retardation of the cement hydration as well as a restriction of crystal growth Ó 2001 Elsevier Science Ltd All rights reserved Keywords: Polymer modi®cation; Microscopic structures; Mechanical properties Introduction The in¯uence of polymer modi®cation on the mechanical and physical properties of mortar and concrete was investigated Dierent parameters were taken into account: type of polymer emulsion, curing conditions and polymer±cement ratio Mechanical testing and scanning electron microscope (SEM) analyses were used to study the structure of polymer modi®ed mortar and concrete The in¯uence of polymer modi®cation on the behaviour and structure of cement mortar and concrete has already been described in literature Dierent models, which de®ne the interaction and the collaboration between the cement and the polymer emulsion, are proposed and brie¯y presented in this paper The results * Corresponding author Tel.: +32-1632-1679; fax: +32-1632-1976 E-mail address: anne.beeldens@bwk.kuleuven.ac.be (A Beeldens) obtained from the tests are discussed in the light of these models Models of structure formation of polymer-modi®ed concrete and mortar 2.1 Properties of polymer emulsion Polymer modi®cation generates an interpenetrating network of polymer ®lm and cement hydrates in which the aggregates are embedded [1] The eect of the polymer modi®cation on the properties of the hardened concrete is in part a result of the formation of this threedimensional polymer network in the hardened cement paste, and in part a result of a lower water requirement for the mixture [2] To reveal the in¯uence of the type of polymer emulsion on the properties of concrete, it is necessary to understand the mechanism of polymerisation and polymer ®lm formation 0958-9465/01/$ - see front matter Ó 2001 Elsevier Science Ltd All rights reserved PII: S - ( 0 ) 0 - 48 A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 Polymer-modi®ed concrete and mortar are most commonly made using a polymer dispersion in water, also called latex A latex consists of small micelles dispersed in water by means of surfactants, and is produced by emulsion polymerisation Emulsion polymerisation takes place in dierent stages [3]: ®rst, monomers are dispersed in a medium (water) by means of surfactants (surface active agents) The surfactant molecules have one hydrophobic end (one or more hydrocarbon chains), the other one being hydrophilic (anionic, cationic or neutral, depending on the group) They are necessary to keep the monomer particles in dispersion since most monomers are hydrophobic due to the hydrocarbon chain The monomers migrate to the hydrophobic tail of the surfactant and electrically charged small droplets, called micelles, are formed Consequently, initiators are added to the continuous phase of the dispersion and activate the monomers in the micelles The result is an emulsion of polymer particles, called latex This emulsion is added to the fresh concrete mixture Once the water of the latex evaporates or is consumed by the cement hydration, the micelles will come closer Finally, the attraction force between the polymer particles will overcome the repellant forces of the surfactants, and the polymer particles will coalesce together into a continuous ®lm This last step greatly depends on the minimum ®lm-forming temperature (MFT) of the polymer emulsion If this temperature is lower than the working temperature, a continuous ®lm will be formed In the other case, no continuous ®lm will appear and the polymer will remain in the material as small spheres, closely packed together A polymer emulsion is characterised by dierent properties The most relevant factors for the use in concrete are the type of monomer, the MFT, the glass transition temperature, the pH, the content of solid parts, the elastic modulus, the elongation at rupture and the stability in a moist alkaline environment of the hardened latex The MFT indicates the temperature at which the polymer particles have sucient mobility and ¯exibility to ¯ow teogether and form a continuous ®lm [4] The MFT is also an indication for the strength of the polymer A high MFT corresponds to a high strength and a ``harder'' polymer [4] The glass transition temperature indicates the temperature at which the polymer transforms from an elastic form to a rigid glass-like form [5] The glass transition temperature is lower than the MFT To illustrate these temperature de®nitions, a styrene± acrylic ester emulsion was poured on a glass plate, and cured at dierent temperatures during several hours The result is shown in Fig The glass transition temperature of this emulsion is )10°C, and its MFT is 32°C When the emulsion is cured at a temperature lower than the glass transition temperature (Fig 1(a)), no ®lm is formed, and a rigid structure visibly consists of small polymer droplets At a temperature between the glass transition temperature and the MFT (Fig 1(b) and (c)), no continuous ®lm is formed again since the energy and the mobility of the polymer particles are still too small to withstand the shrinkage stresses Nevertheless, small pieces of ®lm are formed, each of them showing an elastic behaviour When the ambient temperature during curing is higher than the MFT (Fig 1(d)), a continuous ®lm is formed with elastic properties 2.2 Models describing structure formation of polymermodi®ed mortar and concrete Dierent models have been proposed to describe the structure formation of polymer-modi®ed mortar and concrete (PMM and PMC) The most general and commonly used is the model proposed by Ohama [1] This model can brie¯y be summarised into three steps Immediately after mixing, the polymer particles are uniformly dispersed in the cement paste During the ®rst step, cement gel is gradually formed by cement hydration and polymer particles partially deposit on the surfaces of the cement gel and the unhydrated cement particles In the second step, the polymer particles are gradually con®ned in the capillary pores As the cement hydration proceeds and consequently the capillary water is reduced, the polymer particles ¯occulate to form a continuous close-packed layer on the surface of the unhydrated cement particles and cement gel mixture as well as between the aggregate and the cement paste Ultimately, with water withdrawing due to further hydration, the closely packed polymer particles on the cement hydrates coalesce into a continuous ®lm or Fig Styrene±acrylic ester emulsion cured at dierent temperatures A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 membrane and a monolithic network is formed in which the polymer phase and the cement hydrate phase interpenetrate into each other In addition to this model, Puterman and Malorny [6] indicate some slightly dierent points of view The main dierences are the time at which the polymer ®lm is formed and the in¯uence of the MFT Puterman and Malorny claim that even when free water is still available in the pores, a polymer ®lm can be formed since the polymers adhere to the surfaces of unhydrated cement particles and form there a closely packed layer which can coalesce into a polymer ®lm If the MFT is above the curing temperature, the polymer layer is not a continuous ®lm, but it remains as a thick layer of stacked droplets This layer can thus remain permeable, although it may strengthen and toughen the cement matrix The consequence of this statement is that cement particles can be partly or completely sealed for hydration at the beginning of the hydration process In a later stage, hydration can possibly still take place to result in a microstructure in which the polymer ®lm is incorporated and contained within the cementitious phase This is dissimilar to the model proposed by Ohama in which the polymer ®lm formation takes place after cement hydration and the polymer ®lm is preferably formed in the capillary pores as well as at the transition zone pasteaggregate 2.3 In¯uence of polymer modi®cation on properties of mortar and concrete Polymer modi®cation in¯uences the properties of a fresh concrete mixture as well as the properties of the hardened mixture The fresh mixture is characterised by a reduction in mixing water requirement, a higher air entrainment, improved workability and a retardation eect on the hydration of the cement particles, depending on the type of polymer emulsion The reduction in mixing water requirement and improved workability can be attributed to the presence of the surfactants in the polymer emulsion [2] Surfactants used in the polymer emulsion have possibly also an in¯uence on the cement particles, and cause a better cement particle dispersion in the fresh mixture [2] This improves the workability of the mix, and lowers the water requirement, which on its turn results in a lower water±cement ratio and consequently in reduced porosity and drying shrinkage of the hardened cement paste The higher workability can also be attributed to the ball-bearing eect of the polymer particles in the emulsion [1] Due to this ball bearing eect, the relative movements of the cement particles become easier which results in a more dense material The retardation eect on the cement hydration can be attributed to dierent aspects of the polymer modi®ca- 49 tion First of all, encapsulation of the unhydrated cement particles by the polymer ®lm, as is explained in the model of Puterman and Malorny, may occur This may shelter the unhydrated cement particle from water which causes a partial or complete incapacity to hydrate The retardation can also be due to the retention of the water by the surfactants, since the water of the polymer emulsion is taken into account as hydration water The release of the water could be retarded A third explanation can be found in the lower water±cement ratio A smaller amount of water is present for hydration Furthermore, the migration of the water could be complicated due to the presence of the polymer ®lm The polymer modi®cation of hardened concrete, attributed to the polymer ®lm formation causes the improved adhesion, improved ¯exural and tensile strength, a blocking of the pores that restricts the movement of water and reduces permeability, bridging of microfractures, and toughening of the microstructure The polymer also improves the bond between cement and aggregate particles [2] Part of the mechanical improvement can be attributed to the bridging of microcracks by the polymer ®lm Hence, it is of importance that the polymer ®lm is suf®ciently developed and distributed randomly over the structure However, an increase in tensile strength is also measured on samples modi®ed with a polymer emulsion which has a MFT higher than the curing temperature In this case, the formation of a continuous ®lm is not guaranteed, and the bridging of microcracks is not a sucient explanation for the increase in the strength A reason for the increase could be found in the formation of a more amorphous structure Indeed, the presence of the polymer particles or polymer ®lm prevents the growth of large crystals [7] Large crystals possess less adhesion capacity, not only because of the lower surface area and correspondingly weak van der Waals forces of attraction, but also because the surfaces can serve as preferred cleavage sites [8] One has to take into account that the use of a latex implies not only the presence of polymer particles but also introduces secondary admixtures like surfactants and defoamers to the material which may in¯uence the properties Therefore, a precise characterisation of the latex is necessary Materials A test program was set up to investigate the in¯uence of polymer modi®cation on the properties of cement mortar Dierent parameters were taken into account such as the type of polymer, the polymer±cement ratio and the curing conditions Eight dierent types of 50 A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 Table Properties of the polymer emulsions and w/c ratio applied in mortar Symbol Type of polymer MFT (°C) Solid content (%) w/c SAE PA SB1 SB2 SB3 SB4 SA PV Styrene±acrylic ester Polyacrylic Carboxylated styrene±butadiene Carboxylated styrene±butadiene Styrene±butadiene Styrene±butadiene Styrene±acrylic Vinyl copolymer 32 ( 20 À18 ( À18 ( 20 ( 20 50 28 48 50 45 46 50 40 0.40 0.35 0.35 0.35 0.35 0.35 0.40 0.40 polymer emulsions were tested The properties of the emulsions are given in Table With these dierent types of polymer emulsions, mortars were made with a sand±cement ratio of 3:1 and a polymer±cement ratio of 10% (mass of solid phase of polymer emulsion divided by mass of cement) A river sand 0/5 and cement CEM I/42.5/R (a rapid-hardening ordinary Portland cement) were used The w/c ratio of the dierent mixtures was varied in order to obtain equal ¯ow of 1:61 Ỉ 0:05 measured according to NBN B14-207 The water of the polymer emulsion was taken into account to calculate the w/c-ratio The w/c ratio for the mortars modi®ed with the dierent polymer emulsions is given in Table Testing methods 4.1 Determination of tensile strength of polymer emulsions Prior to the tests on mortar prisms, the tensile strength of the polymer ®lms was measured Therefore, the polymer emulsions were poured on a glass plate with a ®lm thickness of approximately mm After ®lm formation at a temperature higher than the MFT of the polymer emulsion, a 40-mm wide and 150-mm long strip was cut from the ®lm, and subjected to a direct tensile test by an Instron 1026 The tensile test was controlled with a crosshead speed of 0.83 mm/s The tensile stress was calculated taking into account the changing section of the ®lm, presuming a constant volume during the test An increase in length corresponds to a decrease in width and thickness 4.2 Flexural and compressive strength tests Standard prisms, 40 Â 40 Â 160 mm3 , were made with the mortar according to NBN-EN 196 Dierent curing conditions were applied: standard curing conditions (2day moist curing at 20°C and 95% R.H., 5-day water curing at 20°C and 21-day at 20°C and 60% R.H.); dry curing (2-day moist curing and 26-day curing at 20°C and 60% R.H.) and wet curing (2-day moist curing and 26-day water curing at 20°C) After 28 days, all the specimens were stored at 20°C and 60% R.H The ¯exural and compressive strengths, according to NBN-EN 196 were determined after 7, 28 and 90 days of curing as well as dynamic modulus of elasticity, the dry density and the porosity The dry density is measured after drying at 40°C A higher temperature could damage the polymer ®lm The porosity is measured by water saturation after vacuum suction All data presented are average values of three mortar prisms 4.3 Chemical attack test To investigate the in¯uence of sulphuric acid on the structure of modi®ed cement mortar and concrete, samples were subjected to an accelerated degradation test as described by De Belie et al [9] and to an immersion test [10] During the accelerated degradation test, concrete cylinders were mounted on rotating axles Each cylinder is turning through its own recipient with simulation liquid, a 0.5% H2 SO4 -solution by mass, with only the outer 50 mm submersed, at a speed of 1.04 revolutions per hour After each attack cycle, which lasts for six days, the concrete is brushed with rotary brushes, and concrete degradation is measured with laser sensors The experimental results, described more in detail in [10], will be compared with those of the bio-degradation tests with sulphur oxidizing Thiobacillus bacteria, that are actually under development 4.4 SEM observation of microstructures Specimens were prepared for SEM investigation of the microstructure of the polymer-modi®ed mortar After testing of the compressive strength, a small sample of the broken surface was taken, and coated with a gold layer Some samples were, prior to coating, etched with HCl during h and subsequently washed thoroughly with water and dried at 40°C A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 51 Fig Stress±strain curves for the dierent types of polymer emulsions Test results and discussion 5.1 Eect of MFT The results of the tests on the polymer ®lms (Fig 2) indicate that in particular the ®lm of the SAE-polymer emulsion shows a high strength at small elongation, which indeed corresponds to a high MFT [4] The stiening of the SAE-polymer ®lm with increasing stress/ strain can indicate that stronger chemical bonds occur between the polymer particles than for the other polymer ®lms The polymer ®lm made of PA-emulsion showed a small maximum extension and a low tensile strength This is due to a large amount of air voids present in the ®lm Addition of a defoamer to the polymer emulsion could improve the properties of this ®lm 5.2 Strength properties of polymer-modi®ed mortars Fig shows the results of the ¯exural strength measurements The results indicate an increase in the ¯exural strength after 28 days up to 30% for the polymer-modi®ed mortar Only the mortars modi®ed with PA and SA showed much lower results, due to the large porosity Table gives the results of the porosity measurements as well as of the dry density The results indicate a decrease in the porosity due to polymer modi®cation, except for PA- and SA-modi®ed mortars This trend might be a consequence of the measuring procedure Possibly, the very small pores are not ®lled by the water, and therefore the decrease in the porosity could also point at a decrease in the size of the pores, as is mentioned in [1] and not in total porosity In the fu- ture experiments, mercury porosimetry will be done to verify this statement In all cases, the compressive strength after 28-day standard curing is lower than the compressive strength Fig Flexural strength of mortars after dierent times of curing Fig Compressive strength of mortars after dierent times of curing 52 A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 Table Porosity and dry density of the samples cured for 28 days at standard conditions Type of mortar Ref SAE PA SB1 SB2 SB3 SB4 SA PV Porosity (%) Density kg=m3 ) 8.1 2565 4.5 2220 18.8 1173 3.9 2108 5.2 2065 5.9 2030 3.8 2122 20.7 1682 6.3 2140 of the reference mortar (Fig 4) This is due to the retardation eect caused by the polymer modi®cation The compressive strength of the samples modi®ed with SB1 and SAE, water cured during 90 days, is comparable with the compressive strength of the reference mortar The question remains if the SAE emulsion is capable to form an adequate continuous ®lm since the MFT (32°C) is higher than the curing temperature (20°C) SEM investigation revealed a polymer ®lm as can be seen in Fig 5, but this ®lm could be formed during preparation of the sample for the microscopic analysis, since the etched samples were dried at 40°C before coating However, a test on the pure polymer emulsion indicated that no reemulsi®cation nor a retarded ®lm formation is possible once the polymer emulsion is cured at a certain temperature The use of the freeze-drying method in further research will clarify this point The curing of the polymer-modi®ed mortar and concrete involves two steps: cement hydration and polymer modi®cation The sequence in which both mechanisms take place is not yet fully understood Cement hydration is promoted in wet conditions Polymer ®lm formation takes place when water evaporates and is thereby favored in dry conditions This phenomenon is visible in Figs and The ¯exural strength of the samples cured during seven days at dry curing conditions is higher than that of the samples cured at standard curing conditions (2-day moist and 5-day water curing) However, since the compressive strength is mainly determined by the strength of the cement matrix, it is higher under standard curing conditions, and therefore Fig Polymer ®lm in sample with 10% SAE-etched sample standard curing is preferred to dry curing in order to reach a higher compressive strength 5.3 Structure of polymer-modi®ed cement mortar ± SEM investigation The in¯uence of polymer modi®cation on the structure of mortar and concrete is multiple First of all, there are the bridging of the microcracks, the improved adherence of the cement paste to the aggregate and furthermore the reduction of the pore size and of the degree of crystallinity Research done by Afridi et al [7] indicates a change in morphology of the Ca OH2 crystals due to polymer modi®cation In the absence of polymers, the crystals of Ca OH2 are unable to withstand the stresses generated during early hydration, and are therefore distorted to accomodate the spaces formed by the structure of the unhydrated particles and the primary hydration product However, the structure of Ca OH2 produced in the presence of polymer particles is modi®ed to the extent that the crystals become capable of withstanding such stresses, and hence are found without or with little deformation This points out the action of the polymer as a kind of bonding agent between the dierent layers, even in an early stage of hydration In this research, a comparable morphology of Ca OH2 crystals was found as can be seen in Fig for a sample modi®ed with 10% SB1 More developed Ca OH2 crystals are visible, and at a larger magni®cation, some small bridges between the dierent layers can be noticed One of the in¯uences of polymer modi®cation is the strengthening of the transition zone between the aggregate and the paste The transition zone is considered the strength-limiting phase in concrete [8] It is characterized by a larger porosity and a higher amount of oriented crystals Due to polymer modi®cation, the porosity of the transition zone decreases, and additional bridging between the matrix and the aggregate appears When the transition zone of an etched sample is studied, polymer ®lm bridges are clearly visible Figs and present the transition zones of the mortars modi®ed with 10% SA and with 10% SB1 The dierence in porosity is clearly visible This is re¯ected in the results of the strength measurements as discussed before A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 53 Fig Ca OH2 -crystal in sample modi®ed with 10% SB1 Fig Transition zone of sample modi®ed with 10% PA-etched sample The structure of dierent samples, attacked during six cycles of the accelerated degradation test, was inspected by means of SEM As a ®rst conclusion, it can be said that polymer emulsion does not prevent corrosion of concrete by acid attack, but it in¯uences the growth of crystals at the interfaces This can be seen in Figs and 10 Fig presents a transition zone aggregate-paste in an unmodi®ed sample, prepared with CEM III/A/42.5/LA, a blast furnace slag cement Large CaSO4 Á H2 O crystals 54 A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 Fig Transition zone of sample modi®ed with 10% SB1-etched sample Fig Transition zone of unmodi®ed sample after corrosion are visible at the interface Due to the low C3 A content of the slag cement, no ettringite is visible Fig 10 presents a similar transition zone of a sample modi®ed with SB1 The attack on the interface zone is clearly visible, but the crystals which are formed are much smaller This could again point out an encapsu- lation or a binding of the polymer ®lm with the cement hydrates and/or aggregates The presence of polymer in the interfaces improves the cohesion of the material, and thus retards the microscopic erosion Although sulphate corrosion is not stopped, the rate of corrosion showed to be smaller than in non-modi®ed concrete The non- A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 55 Fig 10 Transition zone of sample modi®ed with 8% SB1 after corrosion continuity of the polymer ®lm seems to be the main reason for the further sulphate induced corrosion The eect of continuity or discontinuity of the polymer ®lm, and the relation between chemical and biogenic sulphur attack, are the subject of further research also visible in the corroded samples: at the interface of the unmodi®ed samples, large Ca OH2 crystals are formed For the modi®ed samples, the crystals are also formed, but are reduced in size Further investigation will focus on the durability of the samples Conclusions Acknowledgements Polymer modi®cation of cement mortar or concrete generates an interpenetrating network of polymer ®lm and cement hydrates in which the aggregates are embedded SEM study clearly revealed the presence of a polymer ®lm at the aggregate-mortar interface The density and porosity of the polymer ®lm varied with the type of polymer emulsion Not only the type of monomer is important but also the minimum ®lm forming temperature and the type and amount of surfactants and defoamer added in the emulsion Mechanical tests showed an increased ¯exural strength and a comparable or slightly reduced compressive strength of the modi®ed mortars for most types of emulsions used Two types of latex, however, gave insucient results due to a very large porosity: PA and SA This was also visible from the tests on the pure polymer ®lm A retardation of the cement hydration is noticed This could point out partly or completely the encapsulation of unhydrated cement particles by polymer ®lm, which results in a simultaneous ®lm formation and cement hydration The SEM investigation revealed the restriction on the growth of large crystals by polymer modi®cation This is The authors gratefully acknowledge the ®nancial support from the Fund for Scienti®c Research ± Flanders (FWO) through research grant nr G.0274.98 J Monteny also acknowledges the support of the IWT (Flemisch Institute for the Improvement of Scienti®c Technological Research in the Industry) N De Belie is a postdoctoral fellow of the FWO References [1] Ohama Y Handbook of polymer-modi®ed concrete and mortars, properties and process technology Noyes Publications; 1995 [2] De Puy GW Polymer modi®ed concrete ± properties and applications In: International ICPIC workshop on polymers in concrete for Central Europe, Bled, Slovenia, 1996 p 63±67 [3] Fessenden RJ, Fessenden JS Fundamentals of organic chemistry New York: Harper & Row; 1990 [4] Justnes H, Reynaers T, Van Zundert W The in¯uence of latices and redispersible powders on hydration and strength development of polymer cement mortars In: Sandrolini F, editor Proceedings of the IXth International Congress on Polymers in Concrete, Bologna, 1998 p 225±38 [5] Mewis J Kunststoen cursustekst K.U Leuven, 1994±1995 [in Dutch] [6] Puterman M, Malorny W Some doubts and ideas on the microstructure formation of PCC In: Sandrolini F, editor, 56 A Beeldens et al / Cement & Concrete Composites 23 (2001) 47±56 Proceedings of the IXth International Congress on Polymers in Concrete, Bologna, 1998 p 166±78 [7] Afridi MUK, Ohama Y, Iqbal MZ, Demura K Morphology of Ca OH2 in polymer-modi®ed mortars and eect of freezing and thawing action on its stability In: Cement & concrete composites, vol 12 Amsterdam: Elsevier; 1990 p 163±73 [8] Mehta PK, Monteiro PJM Concrete ± structure, properties and materials New York: Prentice-Hall; 1993 [9] De Belie N, Verschoore R, Van Nieuwenburg D Resistance of concrete with limestone sand or polymer additions to feed acids Trans ASAE 1998;41(1):227±33 [10] Monteny J, Vincke E, De Belie N, Taerwe L, Verstraete W Chemical and microbiological corrosion tests on concrete made with and without addition of polymer In: Proceedings of the International Conference on Infrastructure Regeneration and Rehabilitation, Sheeld, 1999 p 715±24 ... properties of the emulsions are given in Table With these dierent types of polymer emulsions, mortars were made with a sand±cement ratio of 3:1 and a polymer±cement ratio of 10% (mass of solid phase of. .. average values of three mortar prisms 4.3 Chemical attack test To investigate the in¯uence of sulphuric acid on the structure of modi®ed cement mortar and concrete, samples were subjected to an accelerated... zone of sample modi®ed with 8% SB1 after corrosion continuity of the polymer ®lm seems to be the main reason for the further sulphate induced corrosion The eect of continuity or discontinuity of